The present invention relates to Faraday rotators, and more particularly to the magnetic properties of materials comprising Faraday rotators.
Growth of magnet garnets, or Faraday rotators, is well known in the art. Recent interest in Faraday rotators is due to the need for optical isolators and circulators where a non-reciprocal polarization rotation of a linearly polarized light utilizing the Faraday effect in magnetic garnet is required. FIG. 1A illustrates a BH curve of a conventional latched Faraday rotator. As illustrated by FIG. 1A, this Faraday rotator has a large coercivity (Hc greater than 400 Oe), i.e., a large hysteresis loop, and thus requires a large external magnetic field to switch the state of the Faraday rotator. Therefore, this Faraday rotator is used in permanent latching applications in isolators and circulators to reduce the overall size of the devices, and is not suitable for optical switching which requires a small Hc.
FIG. 1B illustrates a BH curve of another conventional Faraday rotator. As illustrated by FIG. 1B, the BH curve for this Faraday rotator is neither linear nor latched. Thus, it is not suitable for use in variable optical attenuators.
Accordingly, there exists a need for an improved Faraday rotator. The improved Faraday rotator should have a small saturation magnetic field. The present invention addresses such a need.
A liquid phase epitaxy method is used to grow the Faraday rotator with a small saturation field (Hs). The Faraday rotator has the formula: Bi3xe2x88x92xxe2x88x92yxe2x88x92zGdxTbyMzFe5xe2x88x92wxe2x88x92nGawPnO12, where M is selected from Y, Yb, Lu, and P is selected from Al, Si, Ge. X, y, w and n are chosen from the ranges of 0.5xe2x89xa6xxe2x89xa61.0, 0.5xe2x89xa6yxe2x89xa61.0, 0.2xe2x89xa6zxe2x89xa60.5, 1.5xe2x89xa6x+y+zxe2x89xa62.0, 0.5xe2x89xa6wxe2x89xa61.0, 0.15xe2x89xa6nxe2x89xa60.5, 0.8xe2x89xa6w+nxe2x89xa61.2. Without M and P, a Type-L Faraday rotator with a linear BH curve is provided, which is well suited for variable optical attenuators. With M and P, a Type-R Faraday rotator with a rectangular hysteresis loop is provided, which is well suited for optical switches. Both are also well suited for use in optical isolators and circulators.